This invention relates to improvements in balloon dilatation catheters for use in angioplasty procedures. Balloon angioplasty procedures have been used with increasing regularity in recent years as a treatment for stenosed arteries, such as the coronary arteries. The procedure involves the use of a special catheter having a balloon at its distal end. The catheter is inserted percutaneously into the patient's arterial system and is advanced and manipulated to place the balloon within the stenosis in the coronary artery to be treated. The balloon then is inflated under substantial pressure to press the plaque and plaque laden arterial wall radially outwardly to enlarge the stenosed region of the artery. When successful, the procedure avoids the necessity for coronary artery bypass surgery.
During an angioplasty procedure, it is not uncommon for the physician to have to make a catheter exchange, to substitute another balloon catheter for the one in place in the patient's artery. The catheter exchange is a somewhat time-consuming manipulation. It involves removal of the guidewire from the catheter and insertion of a long exchange wire into the catheter, then removal of the catheter from the patient by withdrawing it over the exchange wire, then advancing the next catheter onto and along the exchange wire to advance it to the region of the stenosis and then removing the exchange wire. Typically, the exchange wire will be replaced by another shorter guidewire which may be used to facilitate subsequent manipulation and placement of the catheter in the stenosis.
The need for a catheter exchange may be prompted by several factors. Among the situations which requires a catheter exchange are those in which there is a need for a catheter with a different diameter balloon. This may occur, for example, in treating a patient having multiple stenoses either in the same or in different arteries. Because of the nature or size of the stenosis or the size of the artery in which the stenosis is located, it may be desirable to use a catheter with a smaller or a larger diameter balloon than that which is in place in the patient's arteries. Typically, such difference in size of stenoses have required the use of different size balloon dilatation catheters. In recent years, as balloon angioplasty techniques have developed, there has been an increase in the tendency to perform such multiple dilatations on a patient, either to treat multiple stenoses in a single coronary artery or in several of the coronary arteries.
It has been recognized that it would be desirable to have a single catheter having the capability of performing dilatations with different diameter balloons. In one proposed device, the catheter is provided with two dilatation balloons spaced along the length of the catheter, in tandem, with the smaller of the balloons being located distally of the larger balloon. The tandem balloon arrangement presents several difficulties. Because there is a substantial length of catheter which extends distally of the proximal, larger diameter balloon, the range of locations where the proximal balloon can be placed is limited to the more proximal regions of the coronary artery tree. Additionally, the distal end of the catheter which carries the smaller diameter, distal balloon will be too stiff and will not track properly over the guidewire and through the coronary artery.
Another proposal to provide different diameter dilatation capability on a single catheter has been the use of a single balloon having a stepped configuration in which the distal portion of the balloon is of a smaller diameter than the proximal portion of the balloon, with a transition region joining the two. This configuration presents the difficulty that when the smaller diameter of the portion is placed in a stenosis and inflated that also causes the larger diameter portion of the balloon to inflate. If the artery is too small to accept the larger portion of the inflated balloon, that could result in injury to the patient's artery, possibly rupturing it.
It is among the general objects of the invention to provide a multiple balloon dilatation catheter having balloons of different diameters yet which avoids the foregoing and other difficulties.